Method for transform-domain rounding in a decoder and video decoder thereof
a decoder and transform domain technology, applied in the field of digital communication, can solve problems such as drift error, power requirements, drift error,
Inactive Publication Date: 2007-04-19
AVISONIC TECH
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Benefits of technology
"The invention provides a method and decoder for transform-domain rounding to solve the problem of video decoding. The method involves performing motion compensation on a video block, adding an offset to the motion-compensated block, and outputting the result as a rounded reference block. The decoder includes a variable length decoder, inverse quantization module, adder, frame buffer, transform-domain motion compensation module, and offset calculation module. The technical effect of the invention is to improve video decoding quality and efficiency."
Problems solved by technology
This is generally advantageous and tends to lower processor, bandwidth, and power requirements, however, one issue arises: rounding.
Without precise rounding, drift error occurs, drift error being an accumulation of small errors or imperceptible image artifacts into noticeable defects in the video.
In digital video systems this can mean color and shape distortion over a series of frames.
Sometimes drift error is tolerable, however, drift error is usually noticeable and disliked by viewers.
At the heart of this problem is the fact that rounding is a nonlinear operation that is not mathematically commutative with the DCT operation.
This means that truncation can only be performed on values in the pixel domain.
The truncation operations cannot be performed on DCT values, meaning that the positions of the above operations “DCT” and “Truncate” cannot be reversed.
This is not practical from the computational efficiency point of view.
Method used
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[0023] The invention is described in terms of digital video, however, this application does not limit other possible applications for the invention. Also, although the transform domain referenced is of the discrete cosine transform (DCT), other transform domains are also applicable.
[0024] Please refer to FIG. 3, which shows a schematic diagram of a rounding application according to the invention. The process of FIG. 3 is part of a motion compensation process common in Moving Picture Experts Group (MPEG) video playback. Pixel values of a reference block 302 of a video image are required to be calculated. The pixels concerned are those within the square reference block 302 which for the sake of an example, is assumed to be 4 pixels by 4 pixels in size. The reference block 302 is offset from a first source block by 0.5 pixels to the right and 0.5 pixels downward. Since the reference block 302 is offset, three additional source blocks 306, 308, and 310 are required. It can be seen that...
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A method for transform domain rounding in a decoder includes performing transform-domain motion compensation on a block according to a motion vector to generate a motion-compensated block, determining a transform-domain offset with reference to the motion vector, adding the transform-domain offset to the motion-compensated block to obtain an addition result, and outputting the addition result as a rounded reference block.
Description
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to digital communications, and more specifically, to a method for transform-domain rounding in a decoder and a video decoder thereof. [0003] 2. Description of the Prior Art [0004] Video coding is widely used in multimedia electronic devices. Video coding systems normally apply a discrete cosine transform (DCT) to video signals to achieve energy compaction, i.e. compression. Image operations, such as motion compensation and down sampling, have counterparts in the transform domain and so can be performed without decoding the compressed video back into the pixel domain. This can help meet the demands of quality of service (QoS) and power consumption requirements in the ever popular multimedia-capable mobile devices such as mobile phones, PDAs, and portable computers. [0005] Please refer to FIG. 1, which is a block diagram of a conventional decoder 100 for motion compensation in the pixel d...
Claims
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IPC IPC(8): H04N11/02H04N11/04
CPCH04N19/51H04N19/45H04N19/48H04N19/61
Inventor CHEN, CHENWU, PING-HAOCHEN, HOMER H.
Owner AVISONIC TECH